Most organic materials such as plastics, foods, elastomers, fuels, oils, gasoline and lubricants, fibers are susceptible to degradation due to thermal oxidative processes. Harmful, reactive and unstable free radicals are formed during the oxidation process and attack the nearby stable molecules (polymer chains or small molecules) of the materials, “stealing” their electron. The ‘attacked’ molecule loses its electron, resulting itself a free reactive radical to initiate a cascade of chain reactions. Deterioration of their molecular structures as a result of oxidation processes would affect their shelf life, physical and chemical properties. These oxidative reactions are further enhanced at elevated temperatures. The antioxidant molecules are normally added to protect materials against such destructive effects of harmful and reactive free radicals; These antioxidants neutralize these reactive free radicals by donating one of their electrons to stabilize “reactive” free radicals thus stopping the electron ‘stealing’ mechanism.
In many of today's commercial and industrial applications it is desirable to have antioxidants that possess (a) enhanced antioxidant properties, and (b) active and thermally stable at elevated temperatures. Designing of new antioxidants possessing these two desired properties is essential today for the following reasons: The amount of synthetic antioxidant added to some materials, especially in processed food products, is restricted and need to follow Food and Drug Administration (FDA) regulations (for example, 21 CFR 110, 115, 185, 515 and 615, 21 CFR 182.1660, 3169 and 3173, and 21 CFR. 184.1660). In most cases the usage is limited to 0.02% by weight in fat or oil portion of food because some antioxidants such as BHA (butylated hydroxy anisole) and BHT (butylated hydroxy toluene) are suspected to be carcinogenic beyond certain concentration. It is desirable to design new antioxidants possessing enhanced antioxidant activities so that the materials are protected with lower amount of synthetic antioxidants. In the case of other applications, thermally stable antioxidants are required to protect the materials at high temperatures. For instance, many polyolefins and thermoplastics are processed at elevated temperatures. At these elevated temperatures, some of the antioxidants used today are themselves prone to degradation at these elevated temperatures. There is a need for antioxidants that are stable and active at elevated temperatures so that the new antioxidants could be used in high temperature material applications.